Rotary electrical control devices



Jan. 26, 1960 a. A. RALSTON 2,922,975

W ROTARY ELECTRICAL CONTROL mavicxzs Filed Sept. 27, 1957 INVENTOR @W/V/l. 241570 BX; 644/44 l r ATTORNEY United States Patent 2,922,915 ROTARY ELECTRICAL CONTROL DEVICES Gavin A. Ralston, Northport, N.Y., assignor to Micro Machine Works, Inc., Roosevelt, N.Y.

Application September 27, 1957, Serial No. 686,670 '2 Claims. c1. ass-139 This invention relates to novel improvements in rotary electrical control devices, and particularly to potentiometers and switches of the type having a fixed annular member, which may be either'the wire wound resistance element of a potentiometer or the insulating track of a rotary switch, and a rotary contact element arranged to traverse such member in wiping contact therewith.

In the case of potentiometers, the device is ordinarily sold by the manufacturer with the annular resistance element tailored to provide a changing resistance over a fixed angle of rotation, such as 340, of the rotary contact. However, present commercial applications frequently require that the effective angular extent of the resistance of the potentiometer be changed. Thus, a potentiometer in which the effective extent of the resistance element is 290 may be required when the potentiometer is first used, and it may later become desirable to change the effective extent of the resistance to 240, for example. In present commercial practice such wide variations in the specifications to be satisfied by the potentiometer require the user either to maintain an extensive inventory or to place orders very frequently with the potentiometer manufacturer, in which latter case the long lead times ordinarily required by manufacturers poses a serious problem.

The same problem arises in the case of rotary switches, where the moving contact traverses an annular track, one or more arcuate portions of which constitute fixed contacts. As sold by the manufacturer, the annular track might be 360 in extent, with two 50 conductive portions spaced therealong as fixed contacts. Then, the user of the switch may find it necessary to change the extent of one of the fixed contacts to, say 42", or it may be necessary to add a third fixed contact.

There are thus many requirements for rotary electrical control devices of the type referred to which are so constructed that the user can readily change the device to meet particular specifications. It is accordingly a primary object of the invention to provide an improved rotary control device of the type described which is capable of satisfying such requirements.

Another object is to provide such an arrangement wherein the annular member, whether the resistance element of a rheostat or the track of a rotary switch, is related to an annular mounting member in such fashion that a specially formed arcuate electrical conducting element of selected length can be cemented to the mounting member and annular member at any desired location along the annular member.

In order that the manner in which these and other objects are attained in accordance with the invention can be readily understood, reference is had to the accompanying drawings, which form a part of this specification, and wherein: 1

\Fig. 1 is a view in perspective of a specially formed electrical conducting element employed in the invention;

Fig. 2 is an elevational view of said element;

Fig. 3 is a plan view of a potentiometer, less the outer housing, embodying the invention;

a Fig. 4 is a sectional view taken on line 44, Fig. 3, and

Fig. 5 is a sectional view taken on line 55, Fig. 3.

Figs. 3 and 4 being on smaller scale than Figs. 1 and 2, and Fig. 5 being enlarged with reference to Fig. 3.

Referring now to the drawings in detail, Figs. 3-5 illustrate a potentiometer of the general type disclosed in my copending applications Serial Number 560,729, filed January 23, 1956, and Serial Number 575,010, filed March 30, 1956, now Patent No. 2,826,664, issued Mar. 11, 1958. The device comprises an outer annular mounting member 1, an annular, helically wound resistance 2, an actuating shaft 3 and a rotary contact assembly 4.

Mounting member 1 is fabricated from any suitable rigid electrical insulating material, such as a phenolic resinous composition, ceramic, or the like, and includes a body portion having a cylindrical inner surface 5 terminating at one end by a plane, annular, transverse end face 6 and at the other by an inwardly directed, transverse, annular shoulder 7.

The resistance 2 comprises a cylindrical insulating core 8 on which is helically wound the resistance wire 9. Resistance 2 is cemented in place with its outer surface in contact with inner surface 5 of the mounting member and with one end of the resistance seated against shoulder 7. The-axial length of the resistance is such thatthe other end of the resistance projects beyond transverse end face 6.

Actuating shaft 3 is journalled in an insulating member 10 including a flat cylindrical base 11, the periphery of which is cemented to member 1 adjacent shoulder 7, and a cylindrical boss 12 which is concentric with the resistance 2. As seen in Fig. 3, the contact assembly 4 comprises a radially directed arm 13 of insulating material secured to shaft '3 and extending at least to a point adjacent the resistance 2. Secured to the bottom surface of arm 13, as by a rivet or other suitable fastening means at 14, is a sheet metal member 15 including a finger 16 diverging from arm 13 and terminating in a contact tip 17 disposed to ride along the upwardly projecting end of resistance 2. A body portion 18 of member 15 extends below arm 13 inwardly toward shaft 3, terminating in a semi-circular contact portion 19 the tips of which wipe a fixed, circular contact ring 20.

Via a terminal block 20', Fig. 3, electrical connections are made in any suitable fashion to ring 20, to end taps 21, Fig. 3, and to centertap 22, as will be understood by those familiar with otentiometers. As thus described, it is obvious that the effective length of resistance 2 is determined by the position of end taps 21, and is thus about 360.

However, to change this effective length, there is provided a shorting element 23, Figs. 1 and 2. Formed of thin conducting material, such as thin coin silver sheet, the element 23'is arcuate in plan, as seen in Fig. 3, and includes a fiat outer web 24, an intermediate portion 25 of semi-circular transverse cross-section, and an arcuate, dependent skirt 26 joining the portion 25 along the side thereof opposite web 24.

Portions 24, 25 and 26 of the element 23 are so proportioned that web 24 can be fitted flush against transverse and face 6, the skirt 26 then lying in contact with the inner cylindrical surface of the resistance 2, and the intermediate portion 25 embracing the upwardly projecting end portion 2 of resistance 2, as seen in Fig. 5. In such position, element 23 short circuits a corresponding arcuate portion of resistance 2.

Advantageously, the element 23 is secured in place by cementing the same to face 6 and to the appropriate portions of resistance 2.

Though element 23 is preferably formed of very thin sheet metal, such as .003" coin silver sheet, it is advan- 3 tageous to taper the ends thereof, as indicated at 27, Fig. 1.

With element 23 secured in place in the manner illustrated, it will be apparent that the resistance 2 is still electrically Connected to end taps 21, but its effective length is reduced by shorting element 23, so thata max-i mum resistance adjustment is a chievedwhen, as shaft 3 rotates,'contact'2'rides onto element 23. l

Blanks for the elements 23 can be accurately cut to any desired arcuate length by the protractor sheardescribed and claimed in my ,copending application Serial Number 689,406, filed concurrently herewith. The arcuate blank is then formed to the desired cross-sectional configuration seen in Fig. 1, as by use of the apparatus disclosed in copending application Serial Number 686,618, filed concurrently herewith. Thus, having purchased the potentiometer, less shorting element 23, the purchaser is able to produce, at the. site of use of the potentiometer, a shorting element 23 of any pre-selected arcuate length and, by cementing this element in place in the manner seen in Figs; 3-5, the purchaser is able to convert the potentiometer quickly to an entirely different, accurately predetermined maximum resistance. i

4- nular member being mounted concentrically within said mounting member with said outer face in contact with said inner cylindrical surface of said mounting member and with one end of said annular'member seated against said shoulder, the axial length of said annular member being greater than the axial length of said inner cylindrical surface of said mounting member, whereby the other end of said annular member and said'resistance element carried e ex end eyond aidr n ans rs end ac an integral arcuate electrical conducting element having a liat,'transverse outer web portion, anintermediate portion of curved transversecross-section, and an arcuate skirt depending from the 'sideof saidintermediate portion ppw posite said web, said electrical conducting element being mounted with saidweb overlyingsaid plane transverse end surface, said skirt lying in contact with the inner cylindrical surface of said annular member and said intermediate portion embracing an arc of saidother end vof 1 said annular member and said 'helically wound resistance It is apparent that resistance 2 can be replaced by a cylindrical insulating body of the same overall size and configuration as the resistance, the device then being con verted to a rotary switch with element 23 beinga fixed switch contact. In that case, electrical connection is made to the'element 23, as by one of the taps 21, 22. l

I claim: a l

1. In a rotary electrical control device, the combination of an annular mounting member of electrically insulating material, said member having an inner cylindrical surface terminating at one end in a plane transverse end face and having an inwardly directed transverse annular shoulder at the opposite end thereof; an annular support member having cylindrical outer and inner faces and carrying a helically wound resistance element therearound, said an element carried thereon; a rotary actuating shaft disposed coaxially with respect tosaid annular member, and a flexible contact member connected to saidshaft for rotation thereby, said contact memberincluding a contact tip disposed to sweep in wiping engagement successively over said annular member and the resistance element'carried thereon and said" arcuate electrical conducting element as said shaft is rotated. r g f 2; Anelectrical controldevice in accordance with claim 1 and wherein said'arcuate conducting element is cemented to saidtransverse end surface and said annular member.

References Cited inthe file ofthis patent UNITED STATES PATENTS 

